Siloxane Crosslinked Imidazolium PPO/PTFE Membranes for High Temperature Proton Exchange Membranes†

doi:10.7503/cjcu20180721

Abstract

Abstract:

Based on poly(2,6-dimethyl-1,4-phenylene oxide)(PPO), novel high temperature proton exchange membranes were prepared with high phosphoric acid content, superior proton conductivity and excellent mechanical properties. Both methylimidazole(MeIm) and triethoxysilylpropyldihydroimidazole(SiIm) were used as functional reagents to graft the imidazolium groups onto the PPO polymer, in which the imidazolium group provided the phosphoric acid interaction sites. Meanwhile crosslinking of the modified PPO was achieved by forming a crosslinked silane network via the hydrolysis reaction of SiIm in an acidmedium. Moreover, porous poly(tetrafluoroethylene)(PTFE) was used as the membrane matrix toenhance the dimensional stabilities and mechanical strength of the fabricated membranes. Physicochemical properties of composite membranes with various crosslinking degrees were investigated accordingly. The results showed that the PPO-SiIm-MeIm/PTFE composite membranes possessed dense structure, superior thermal stability, improved chemical stability, high conductivity and suitable mechanical strength simultaneously. As an example, the PPO-50%SiIm-50%MeIm/PTFE membrane with a phosphoric acid doping content of 242.5% exhibited a conductivity of 0.09 S/cm at 160 ℃ under no humidification conditions, and a tensile strength of 3.6 MPa at room temperature. The results indicate that PPO-x%SiIm-y%MeIm/PTFE membranes have the potential to be used as HT-PEMs.

Key words: High temperature proton exchange membrane, Poly(2, 6-dimethyl-1, 4-phenylene oxide), Porous poly(tetrafluoroethylene), Imidazolium functionalization, Siloxane crosslinking

CLC Number:

O631
O646

TrendMD:

REN Xiaorui,LIU Chao,LI Huanhuan,YANG Jingshuai,HE Ronghuan. Siloxane Crosslinked Imidazolium PPO/PTFE Membranes for High Temperature Proton Exchange Membranes^†[J]. Chem. J. Chinese Universities, 2019, 40(5): 1089.

Figures/Tables 8

Scheme 1 Preparation procedure of PA doped PPO-MeIm-SiIm/PTFE composite membranes

Fig.1 FTIR-ATR spectra of BPPO(a), PPO-100%SiIm/PTFE with hydrolysis(b) and PPO-100%SiIm-Un/PTFE without hydrolysis(c) and PPO-50%SiIm-50%MeIm/PTFE membranes(d)

Fig.2 SEM images of the surface of PTFE(A), PPO-50%SiIm-50%MeIm/PTFE(B) and PPO-100%SiIm/PTFE membranes(C), respectively, the cross-section of PTFE(D) and PPO-50%SiIm-50%MeIm/PTFE membranes(E) and EDX element analysis in the selected area for the cross-section of PPO-50%SiIm-50%MeIm/PTFE composite membrane(F)

Fig.3 TGA curves of BPPO(a), PPO-40%SiIm-60%MeIm/PTFE(b), PPO-60%SiIm-40%MeIm/PTFE(c), PPO-100%SiIm/PTFE(d) and PTFE membranes(e) at a heating rate of 10 ℃/min in air

Fig.4 Fenton test results of various PPO-SiIm-MeIm/PTFE membranes in 3%(mass fraction) H2O2 solution containing 4 mg/kg Fe2+ at 68 ℃a. PPO-100%SiIm; b. PPO-100%SiIm/PTFE;c. PPO-60%SiIm-40%MeIm/PTFE; d. PPO-40%SiIm-60%MeIm/PTFE; e. PPO-100%MeIm/PTFE.

Table 1 Acid doping content and swellings of various membranes after immersing in 85%(mass fraction) PA solutions at 60 and 120 ℃

Membrane	Mass fraction of PA(%)		S(%)		V(%)
Membrane	60 ℃	120 ℃	60 ℃	120 ℃	60 ℃	120 ℃
PPO-40%SiIm-60%MeIm/PTFE	267.5	312.7	68.0	80.0	197.5	210.6
PPO-50%SiIm-50%MeIm/PTFE	242.5	—	45.0	—	150.0	—
PPO-60%SiIm-40%MeIm/PTFE	237.5	253.4	39.0	68.0	110.0	145.6
PPO-70%SiIm-30%MeIm/PTFE	232.0	—	39.0	—	102.5	—
PPO-100%SiIm/PTFE	158.0	162.7	26.5	44.0	86.0	94.5

Fig.5 Conductivities of acid doped PPO-SiIm-MeIm/PTFE membranes as a function of temperatures without humidifyinga. PPO-40%SiIm-60%MeIm/PTFE/PA; b. PPO-50%SiIm-50%MeIm/PTFE/PA; c. PPO-60%SiIm-40%MeIm/PTFE/PA; d. PPO-70%SiIm-30%MeIm/PTFE/PA; e. PPO-100%SiIm/PTFE/PA.

Fig.6 Tensile stress-stain curves of acid doped PPO-SiIm-MeIm/PTFE membranes at room temperaturea. PPO-100%SiIm/PTFE; b. PPO-70%SiIm-30%MeIm/PTFE; c. PPO-60%SiIm-40%MeIm/PTFE; d. PPO-50%SiIm-50%MeIm/PTFE; e. PPO-40%SiIm-60%MeIm/PTFE.

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